In poker slang, the term brick refers to a card that fails to improve your hand on the turn or the river. Hence, it has a negative connotation, as it most often causes you to lose the pot.
In most cases, a brick is just a random card that doesn’t affect anyone’s range, meaning that it’s the complete opposite of an action card.
For example, let’s say you have a 5 and a 6 in your hand. The flop comes up 7, 8, Q. You bet and your opponent calls. The fourth street brings a brick card in an offsuit 2. All you and your opponent can do is check and just get to the river.